This disclosure relates to novel aqueous ink-jet inks containing an aqueous vehicle, a colorant, a first organic co-solvent and a second organic co-solvent for improving ink adhesion to print substrates. Also disclosed is a printing method using these inks.
Inkjet recording is a printing method wherein droplets of ink are ejected through fine nozzles to form letters or figures on the surface of recording media. Inks used in such recording are subject to rigorous demands including, for example, good dispersion stability, ejection stability, and good fixation to media.
Aqueous dispersions of pigment particles are widely used in ink-jet printing. Because a pigment is typically not soluble in an aqueous vehicle, it is often required to use a dispersing agent, such as a polymeric dispersant or a surfactant, to produce a stable dispersion of the pigment in the aqueous vehicle. More recently, so-called “self-dispersible” or “self-dispersing” pigments (hereafter “SDP(s)”) have been developed. As the name would imply, SDPs are dispersible in water without dispersants.
The main advantage of inkjet printers over laser printers includes low cost and simplicity. However, many commonly formulated inkjet ink do not dry adequately when printed on hydrophobic media that have not been specially treated to accept water-based inks, consequently resulting in poor image quality. Hydrophobic media include resin-coated papers such as those used for conventional printing, transparency films made of acetate and untreated vinyls. However, treatment of hydrophobic media to accept water-based inks causes increases to both printing costs and processing time.
U.S. Pat. No. 5,165,968 discloses water-based inks containing a small amount of lower alkyl alcohol(s) or benzyl alcohol to decrease dry time and improve smear resistance of printed image.
U.S. Pat. No. 6,277,183 discloses aqueous inkjet inks containing a long chain alcohol having at least 8 carbons to reduce mottle and halo of printed images.
U.S. Patent Application Publication No. 2003/0079649 discloses aqueous black inks containing one 1,2-diol, a mono- or di-hydric alcohol for printing on glossy media with increased dot size and reliability.
A need exists for an inkjet ink that can be printed on hydrophobic media to provide a high quality image without having to pre-treat the surface of the media or using a large amount of water-soluble solvents that can lead to degradation and/or delamination of pen components. The present disclosure satisfies this need by providing ink compositions having a desirable balance of organic co-solvents for both wetting the media and aiding the penetration of inks into the media for drying while maintaining the stability of the inks, good pen firing and material compatibility.